High-frequency signaling system



Aug. 16, 1927; 1,638,925

L. ESPENSCHIED HIGH FREQUENCY SIGNALING SYSTEM Filed Aug. 16, 1922 IN VEN TOR.

ATTORNEY Patented Aug. 16, 1927.

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Application filed August 16, 1922. Serial No. 582,256.

This invention relates to high frequency signaling and especially to a method 'a'nd. means for effecting high frequency carrier transmission hy'wire or radio, which is char-- acterized by the manner in which the carrier current is derived? Instead 'of being generated locally and independently at the transmitting station, these Oscillations are set up asth result of high frequency singing around the complete circuit including trans mitter and receiver. Y

'Briefiy, theinvention consists in the, use of carrier oscillations received at one station from the remote station to controlthe generation of carrier oscillations at the first station, these latter to be picked up at the remote station to control. the generation ofcarrier oscillations that station. The system is adapted for signaling in the two directions on the same frequency or on different fre: quencies, as will appear lateri' Reference may he had to the accompany ing drawings in which Fig. I is a circuit illustrating, the'application of this invention to radio signaling; Fig 2 is a modification of the circuit ofFig. 1:. and Fig. 3 is a'detail of part of the circuitin'caseit' is to be applied to, ire signaling] Referring more particularly to Fig. 1, there is shown a completesignaling system comprising the necessary equipment at two stations, A and B. At the station A there is a radiating antenna 5 adapted to transmit modulatid carrier oscillations of frequency f the oscillations for this transmission heing obtained from the ontnut circuit of, an amplifier modulator 7. obtain such modulated high frequenciesfit: is necessary to supply the message which is to he trans-- mitted and also the high frequency oscillations Which are to act as the carrier; 'The first of these comes over the line L through the standard hybrid coil 9. used for duplex telephony, the incomingsneech'message being impressed on the modulator-'7. At the same time there is impressed on this modulator high'frequency carrier oscillations from an amplifier 10.

One of'the main features of my invention consists in the manner in which oscillat ons are obtained for the "amplifier 10. The

method! consists in receiving on an antenna, which, in this ca e, I have shown as a loop antenna R oscillations of carrier freqency 7% mm" t e were and using these re.

ceived signals to control the generation of the necessary high frequency oscillations for the transmitter 55. In this case the re ceived oscillations of carrier frequency] are combined with locally generated oscillations' of frequency f from the oscillator 12 in the modulating'devic'e 13. V In accordance with the Well'knoivh pronerty ofa modulat' ing'de'vice, there will appear in the output of th' e*modulator l3 frequencies equal tothe sum and to the difference of the oscillations f and One of these oscillations, such foreXample,as is then amplified by the amplifiers 14 and 1 0 to as great an extent is necessary, being then used as the primary source ofoscillations'for the modula- The signals received on the antenna R are, in general modulated With the message to be receivedat'that stat'ion'yand. in addi tion to the'carrier frequency f there will, in general, be present; the side hands f 'ii-s where 5 represents theaudi'ofrequency of the message to he received. It" is'impormnt',of cou'rsej,to eliminate these side fietirienci'es, and I therefore insert filters '15 and16, prefer ably of the hand-passing type; hich'are so adjusted'as to permit the passage of the'ca r ri'er frequency f "but to eliminate all other frequencies. Obviously. instead "of using Wave filters such as shown. it would he feasible toflsuhstitiite sharply'tuned circuits which are; responsive to" substantiallyone frequency onlyl Ait times it will also be convenient to shift the phase of the highfre' qnency oscillations impressed "on the modulator 7, and for this purpose it is convenient to introduce aphasia-shiftingdevice 1 8.

l The generating apparatus at the'stati on B is identically ence between the receii ed and the locally generated oscillations is used 'ratherthan the summation "frequency, itheih'g understood that the local generator at-the "station B "is" held to the same frequency i as the local' generator at the station A. Thus \vhenoscillations have been initiated ati'the station A," v quency f these W ill"h'e received "on the receiver li atthe station B and combined with the: local oscillations to yield a frequency ,"'Which inayhe given the designation f After suitable" filtering and amplification, this derived frequency is raditttedfrom the station B aridre eived 'atfR the same, except that 'the' differ?- radiating a the 'freof station A. There it is combined with the locally generated oscillations f yielding f d-f which, it will be noted, is equal to f,, the frequency radiated from station A. Thus a complete cycle is set up, tending, under suitable conditions, to maintain itself. F or the purposes of receiving the signal message, I have shown in Fig. 1 at station A a second antenna R of the loop type, which will also pick up the signal from the station B, whose carrier frequency is f,. Thissignal may be treated in the usual manner to yield the signal message, such for example, as being impressed on a detector 20, passed through a suitable filter 1 and amplified in the device 22, whereupon it may be impressed on the hybrid coil 9 for transmission over the line L. A corresponding arrange ment for reception is shown at station B. To initiate the generation of oscillations, it is necessary to send out a train of waves from the one station or the other. For this purpose, I may resort to a shock excitation of one station or the other, but if this is not sufficient, I may use at either or both stations a small generator of suitable carrier frequency. At station B, for example, this would comprise a local generator of oscillations 25 of frequency f,, which may be of sufficient amplitude so that when connected to the modulator 7 of station B full amplitude oscillations will build up for radiation from the antenna 6. Having started the system in operation, however, this oscillator may then be dissociated. It will be important, of course, in this connection to have the oscillations derived fromthe receiver in phase with the oscillations from the generator 25, and for this purpose it will be convenient to use the phase-shifting device 18 mentioned above. Also to indicate that synchronism has been obtained, it will be desirable to have some synchronizing indicating instrument associated with the system, such, for example, as 26, shown at station B.

It is apparent that suitable precautions must be used to prevent the singing of one station on itself, that is, oscillations picked up at R, of station A from its own radiating antenna 5 must be sufficiently small in in tensity, so that oscillations of the corresponding frequency are not set up thereby. To this end, a number of expedients may be used. One obvious expedient is to have the antenna R fairly well removed from the antenna 5, and also to have it of such a form as'to be strongly directional. It should then be so orientated as to show least sensitivity to its own radiating antenna. This is readily accomplished in the case of the loop antenna by placing the plane of the loop at right angles to the radial line from the antenna 5 to the loop. At the same time the loop may be so located as to show maximum sensitivity to the waves from the remote Sta/- tion. The eiiectof the transmitter upon its own receiver is also reduced in the case illus trated by virtue of frequency selection, as Well as directional selection, the transmitting and receiving frequencies being materially different. The necessary condition is that the gain through the radio circuits, consisting of the receiver amplifier 14: and the transmitter power amplifier 10, shall be greater than the loss between the transmitter 6 of station B and the receiver R, of station A. Also the loss between the transmitter 5 of station A and the receiver R, of that station shall be greater than the gain of the amplifiers 14 and 10. The same conditions apply to each terminal.

In the figure thus described, transmission takes place in one direction on one frequency and in the other direction on a different frequency. The system may be devised to transmit in both directions on one frequency. Referring to Fig. 2, station A is shown as comprising the radiating antenna .T and the re ceiving antenna R which latter is preferably of the loop antenna type or other highly directional form of antenna. At the station B there is a corresponding radiating antenna T and receiving antenna 3,. Oscillations of carrier frequency 7 from the an tenna T, are picked up at the station A by the antenna R,. A portion of the energy is tr nsmitted to a detector D from whence, :111'61 suitable amplification and filtration, the detected message is transmitted over the line L. A portion of the energy received on the antenna R, is sent through a different channel, con'iprising a band filter 80, which permits the passage of the carrier frequency only, eliminating, in particular, the side bands of the received wave. After suitable amplification in 31, the oscillations are impressed on the grid of a power amplifying system 32, of a form now well known in the art, and comprising a vacuum tube amplifier with suitable source of power G. The power delivered by this amplifier 32 to the radiating antenna T maybe controlled in accordance with the message to be transmitted by means of a n'iodulator which receives the signal in the usual way from the line L through the hybrid coil 34;.

The station B is identical to the :"tation A, and, as a result, each station is adapted to generate oscillations of the carrier frequency, the generation of these oscillations being controlled by the reception of oscillations of this same frequency from the remote station.

Here, also, it is important that the generation of oscillations shall not be controlled by the radiation from one antenna, being picked up by the receiver of the same station.

In other words, the condition must be fulfilled that the gain through the radio circiated apparatus.

units, consistin of the amplifiers 31 aiid'32 of station A, shall be greater than the loss between the transmitter T and the receiver R,. Also, the loss between the transmitter and the receiver R, shall be greater than the gainfrom the amplifiersfil and 32.

I While I have described the invention as relating especially to radio signaling, it is, of course, apparent that it is equally well adapted for high frequency signaling on wires. Fig. 3 shows one method for asso' ciating the apparatus of onestation with the transmission line in order to obtain the desired results. For example, the power to be transmitted and coming from that portion of the apparatus corres ionding to 32 of Fig. 2 is impressed on a: balanced hybrid coil 40, which has associated with it the balancing network N and the line L'. To the conjugate points of the coil {L0 is connected the receiving apparatus, comprising, if desired, an amplifier ll, the circuit then leading to the detector D, as shown in Fig. 2, and to the filter 30 of the same figure, the portion of the energy passing through the filter '30 being used to control the power transmitted through the circuit 32. Since the coil 40 is balanced,

power coming from the circuit 32 produces no effect on the amplifier 41 and itsasso- On the other hand,- the high frequency signal coming from the line L is; transferred, through the amplifier 41, to

its associated apparatus, whereupon it performs the same functions as described in connection with Fig. 2. I

' Many variations may be made in the circuit which are shown for illustrative purposes only. For example, in Fig. 2 I have shown .at each station one receiving antenna only, whereas in Fig. 1 two: such anten-nae are shown, one to pick up the energy for the interpretation of the message andthe other for the control. Obviously, in Fig; lpthese two antennae could be combined into one,

as in Fig. 2, and, onthe other hand,- ifdesired, two separate receiving antennae may be used in Fig. 2.

lVhat is claimed-is:-

1. In a high frequency signaling system involving- -a pair of intercommunicating stations, each having a receiver and a transmitter but including no means for independently generating carrier oscillations, the

pinethod of deriving carrier currents for duplei' s1gnal1ng,which consists n setting up a singing condition betweenthe two stations, whereby carrier oscillations are automatically emitted from each station, modulating the oscillations at each station with the message to be transmitted and detecting these at the other station.

2. In a high frequency signaling system, the method of deriving carrier currents for duplex signaling, which consists in receiving signals from one station on a carrier frequency, combining with said carrier frequency a locally generated frequency to yield a sum and difference frequency controlled by the received frequency, amphfyiiig one of the controlled frequencies and transmittr g it back to the other station.

3. In a high frequency signaling system, the method of deriving carrier currents for duplex signaling, which consists in receiving signals from one station on acarrier frequency, combining with said carrier frequency a locally generated frequency to form a sum and a difierence frequency, amplifying one of these, modulating it and transmitting it back to the other station.

.4. In a high frequency signaling system, a pair of intercominunicatin 'stations each comprising a'circuit for receiving modulated carrier oscillations from the other station, a circuit for receiving a portion of said oscillations and adapted to suppress all but the carrier frequency of the received oscillations, and means whereby said carrier frequency is caused to control the generation of oscillations for transmission in the reverse direction to the other station.

control the generation of oscillations for transmission'in the reverse direction to the other station.

(3. In a high frequency signaling system, aparr of intercommumcating stations each comprising a receiving circuit and a generator of oscillations. means for causingoscillatronsreceived from the other StittlOIl to control the generation by said generator of oscillations for transmission in the reverse direction to theother station, and a second circuit for receiving a portion of the incoming oscillations-and means in said second circuit to detect thenr to the signaling frequency. V

7. In a high frequency signaling system, a circuit for receiving modulated high frequency oscillations from a remote station, a local generator of oscillations. means'for combining the received and the locally gen erated oscillations to a sun) and a difference frequency controlled by the: received frequency, means for amplifying one'of these and transmitting it back to the other station.

8. Ina high frequency signaling system, a circuit for receiving modulated high frequency modulated carrier oscillations from a remote station, a circuit for receiving a portion of said oscillations, means for filtering out therefrom all but the carrier frequency, a local generator of oscillations, means for combining the received and locally generated oscillations to a sum and adifference frequency controlled by the received frequency, means for amplifying one of these and transmitting it back to the other station, a second circuit for receiving another portion of the received oscillations and adapted to detect them to the signaling frequency. 7

9. In a high frequency signaling system involving a pair of intercommunicating stations, each having a receiver and a transmitter but including no means for independently generating carrier oscillations, the method of deriving carrier currents for duplex signaling which consists in setting up a singing condition between the two stations whereby carrier oscillations are auto matically emitted from each station.

. 10. In a high frequency signaling system involving a pair of intercommunicating stations each having a receiver and a transmitter but including no means for independently generating carrier oscillations, the method of deriving carrier currents for duplex signaling, which consists in producing a condition such that the loss in trans mission from the transmitter of one station to the receiver of the other will be less than the gain intransmission from the receiver of one station to the transmitter of the same station whereby carrier oscillations are automatically emitted from each station.

11. In a high frequency signaling system involving a pair of intercommunicating stations each having a receiver and a transmitter but including no means for inclependently generating carrier oscillations, the method of deriving carrier currents for duplex signaling, which consists in producing a condition such that the loss in transmission from the transmitter of one station to the receiver of the other will be less than the gain in transmission from the receiver of one station to the transmitter of the same station and the loss in transmission from the transmitter of a station to the receiver at that station will be greater than the gain in transmission from the receiver to the transmitter whereby carrier oscillations are automatically emitted from each station Without causing singing between the transmitter and receiver of each station.

12. In a high frequency signaling system, a pair of intercommunicating stations each comprising a receiver and a transmitter but including no means for independently generating carrier oscillations, a circuit at each station for transmitting currents received by the receiver to the transmitter and amplifying means in said circuit, the transmission conditions of the system being so adjusted that the loss in transmission from the transmitter of onestation to the receiver of the other will be less than the gain in transmission from the receiver to the transmitter of a given station whereby carrier oscillations will be automatically emitted from each station.

13. In a high frequency signaling system, a pair of intercommunicating stations each .comprising a receiver and a transmitter but including no means for independently generating carrier oscillations, a circuit at each station for transmitting currents received by the receiver to the transmitter and amplifyingmeans in said circuit, the transmission conditions of the system being so adjusted that the loss in transmission from the transmitter of one station to the receiver of the other will be less than the gain in transmission from the receiver to the transmitter of a given station, while the loss intransmission from the transmitter to the receiver of a given station will be greater than the gain from the receiver to the transmitter whereby carrier oscillations will be automatically emitted from each station without producing singing between the transmitter and receiver of each station.

14. In a high frequency signaling system, a pair of transmitting stations, each station including separate transmitting and receiving antennae, local circuits for connecting the receiving antenna of each station to the transmitting antenna thereof, said local circuits and antennae being incapable of independently generating oscillations. means to set up a singing condition between the two stations over a path from the transmitting antenna of one station to the receiving an tenna of the other station, from the receiving antenna of the other station to the local transmitting antenna thereat, from said local transmitting antenna to the receiving antenna of the first station, and from the receiving antenna at the first station to the transmitting antenna thereat, means to modulate, in accordance with signals, the oscillations transmitted from the transmitting antenna at one station to the receiving an tenna at the other station as the result of said singing condition, and means at each station to detect the signals so transmitted.

In testimony whereof, I have signed my name to this specification this 14th day of August, 1922.

LLOYD ESPENSGHIED. 

